Cryo-EM structure of the Shigella type III needle complex
Fig 3
Structure of the periplasmic IM ring.
The periplasmic IM ring model in cartoon representation (MxiG subunits in blue and violet, MxiJ subunits in orange and beige). (A) Top view (left panel) and tilted view (right panel) of the periplasmic IM ring composed by 24 copies of MxiG and MxiJ subunits forming two concentric rings. The inner membrane is located below the ring. (B) Side view of one MxiG and one MxiJ neighboring subunits. Only the periplasmic domains are shown and labeled. Secondary structure elements involved in IM ring interactions are also labeled. The domains adopt RBM αββαβ topology, except the D1 domain of MxiJ that has inverted RBM βαββα topology. (C-E) Interacting subunits of the IM periplasmic ring: one MxiG between two MxiJ subunits (C), a couple of neighboring MxiG (D) and MxiJ subunits (E). Secondary structure elements involved in IM ring interactions are labeled.